Australia’s coastal and marine regions support a large range of species, many of them found only in Australian waters. The marine environment is also important to Australian society and the economy. Many of the ways in which we use our oceans, beaches and estuaries can affect the quality of the ocean’s water and the diversity of life within it.

There are very few nationwide time series data suitable for assessing the progress of Australia's marine ecosystems. At some time in the future, perhaps, betterprogress indicators might become available. For the time being, this commentary:

recognises the importance of the ocean

describes some of the important influences on the health of our seas (such as fishing, introduced species and water quality).

However, it does not attempt to assess overall progressamong Australia's marine ecosystems.

Australia has one of the longest coastlines of any country. The Exclusive Economic Zone, the area surrounding Australia's coast for which Australia has exclusive responsibilities and to which it has exclusive rights, covers 11 million square kilometres (among the largest of any country in the world). And so it is perhaps not surprising that beaches, estuaries and wider marine ecosystems play an important role in Australian life.

Australia's oceans are diverse, ranging from tropical seas, through temperate to polar waters; and from shallow coastal waters to ocean trenches that are six kilometres deep. This diversity is reflected in a vast array of life forms. More than 4,000 species of fish live in Australian waters, and about one-quarter of them are found nowhere else (most of these are found in southern waters). Australian waters provide a home to at least 43 species of whales and dolphins and 112 species of seabirds. Australia has the world's largest and most diverse area of seagrasses, largest area of coral reefs and highest diversity of mangrove species.1 Much remains to be discovered: a research expedition in 2003 over the Norfolk ridge to our eastern seamounts found more than 1,800 species, many new to science.2

There are substantial pressures on Australia's marine environment. Over 80% of the population live within 50 kms of the coast,3 and 97% of the volume of Australian trade is carried by ships.4 In 2001-02 Australian fisheries produced about 233,000 tonnes of fish5 while in 2002-03, about 650,000 people visited the Great Barrier Reef, more than 160,000 of whom were from overseas.6

Fishing, particularly overfishing, places strains on a number of species, and may also affect other species through disruptions to the food chain or accidental catching of other fish, birds, mammals, and turtles. The release of hydrocarbons, waste water and other nutrients can also disrupt marine ecosystems, while the introduction of foreign species into Australian waters has the potential to cause irreversible harm.

To assess progress within our oceans and estuaries one would need information on a broad range of issues, and how they are changing over time. The oceans are vast and for many areas, information is scarce, so a thorough assessment of progress is not yet possible. Some data are available for some important concerns, particularly for the coastal and estuarine environment and these are discussed here. The National Oceans Office is currently gathering a range of relevant data and developing indicators. These should be available for future editions of this publication.

Estuaries

The Estuarine Condition Index is an indicator that has been developed by the National Land and Water Resources Audit (NLWRA). Time series data are not available yet, but in future this index will go a long way towards summarising progress in our marine ecosystems. The index assesses the condition of about 1,000 estuaries around the Australian coast. Because estuaries occur at the borders of marine and freshwater ecosystems, they are influenced by the tides and also by fresh water from the land. And so measuring the condition of estuaries not only reports on the state of our oceans; it sheds light on how land use around the water that flows into the estuary is affecting the sea. The more modified an estuary the greater the pressures on it; in 2002 the NLWRA assessed estuary conditions as:7

near-pristine - 50%.

largely unmodified - 22%.

modified - 19%.

extensively modified - 9%.

Fish and fishing

Australia's major fisheries target high value species such as lobsters, prawns, abalone and tuna, which, despite their modest tonnage in world terms, are subjected to high fishing pressure.8

An underfished stock could sustain catches higher than those currently taken. A fully fished stock is one where current catches and fishing pressure are close to their sustainable limit - increasing the fishing pressure or catches may lead to overfishing. A 'heavily fished' stock may be overfished; it is clear that fishing is intense, but not clear whether it is excessive. A stock is overfished when there is too much fishing or when there are too few fish left; in the latter case, the stock may reflect the effects of previous excessive fishing - management might curtail overfishing, but it can take some time (perhaps many years for some species) before a stock recovers.

A review of the status in 1999 of Australia's primary fishery stocks managed by Australian governments indicated that of the 145 species considered, nine were underfished, 35 fully fished, 15 heavily fished (some of which were probably overfished), and 17 overfished. The review was uncertain about the status of the other 69.8 Data on those fish stocks managed by the Australian Commonwealth was updated in 2002, and found that 16 of the 75 principal species managed by the Australian Commonwealth were classified overfished compared to only five a decade ago.9

Fisheries production, value and employment, by state - 2001-2002

Production

Weight

Value

Employment

tonnes

$m

no.

NSW

22 304

136

4 002

Vic.

9 211

117

2 070

Qld

31 634

277

4 311

SA

37 412

490

2 899

WA

33 956

615

3 229

Tas.

22 912

327

2 573

NT

5 763

37

509

Commonwealth

75 387

481

. .

Total

233 346

2 409

19 627

Source: Australian Bureau of Agricultural and Resource Economics. (Total includes minor amounts not shown).5

Australian FisheriesThe gross production of Australia’s fisheries in 2001-02 was about 233,000 tonnes, valued at $2.4 billion (including the value of aquaculture, which contributes 30% of the total). Fisheries managed by the Australian government produced 75,400 tonnes, valued at $481 million in 2001-02. The Northern Prawn, Eastern Tuna and Billfish, South East and Southern Bluefin Tuna fisheries provide three-quarters of that value.9

State and territory managed commercial fishery production reached 158,000 tonnes in 2001-02, with a value of $1.9 billion. Australia’s most valuable fishery is the State managed Western Rock Lobster Fishery. Other important state/territory managed fisheries - for abalone, southern rock lobsters and prawns - rely on long standing, valuable export markets. There are also many coastal, estuarine, freshwater and aquaculture fisheries supplying a diverse range of finfish and invertebrates for the fresh fish market.9

Comparable information at a state level is not available, but it is clear that some state managed fisheries are also subject to heavy fishing pressure. Curbing excessive fishing and rebuilding overfished stocks are fundamental to the long-term viability of fisheries.

The status of most of the species caught incidentally to primary species is uncertain (even the status of those species caught incidentally that contribute substantially to the market value of a fishery). In fisheries where a bycatch of threatened or endangered species occurs, the introduction of bycatch action plans (mandatory for fisheries managed by the Australian government) has increased protection from fishing. For example, Northern Prawn Fishery vessels must use turtle-excluder and bycatch-reduction devices.9

A decline in catch can point to increasing scarcity. It can also point to reduced fishing effort. But if catch sizes have remained constant while the effort required to catch fish has increased, the size of the fish stocks may also have decreased. In the South East Fishery, the annual catch remained relatively constant between 1992 and 2002, yet required double the amount of trawling by the late 1990s.9

Whales and DolphinsThe importance of some whale and dolphin species to the Australian public is reflected in the popularity of activities such as whale watching. The hunting of whales for meat and oils was common in Australian waters from the early 1800s to the mid-1960s. An estimated 26,000 Southern Right Whales were taken from south-eastern Australia and New Zealand before they were protected in 1935, and over 40,000 Humpback Whales were killed in Australia and New Zealand before they were protected worldwide in 1965.10

Whales have low birth rates, and their numbers are slow to recover. But conservation efforts have seen numbers of Humpback Whales grow at 10% per year, moving them in 1998 from a Commonwealth endangered species to a vulnerable one. Other species, like Blue and Southern Right Whales, remain listed as endangered.11

TurtlesOf the seven species of marine turtles found in the world, six breed in Australia, although their population numbers are uncertain.

Turtles migrate which makes them susceptible to both international and domestic pressures. The eastern Australian Loggerhead Turtle (Caretta caretta), breeds almost exclusively in the southern Great Barrier Reef region and is an endangered species. Its nesting population has declined by 70%–90% since the 1970s, to about 300 animals.11 Threats to turtles include bycatch in trawl nets, traditional hunting, habitat degradation, bycatch in shark control programs, floating rubbish (plastic and fishing lines) and prawn and other fishing activities. Regulation on turtle hunting and Bycatch Action Plans are some of the initiatives taken to protect marine turtles in Australia.11

Introduced species

Fishing is not the only human activity that affects the biodiversity of Australian waters. Introduced organisms can place native species at risk from predatory behaviour or competition for food. More than 250 species are known to have been introduced into Australian waters. Most are not believed to pose a large threat, but a few have substantially altered habitats and ecosystems.12

The accidental introduction of organisms can occur via ballast water. When a ship's hold is empty, ballast water is taken on board to balance the ship. When the ship next loads cargo at port, the ballast water is discharged along with any organisms living in it. In 2001 Australia introduced new regulations making it mandatory for vessels entering Australian waters to undertake some form of treatment of ballast water before discharging it in any Australian port.

SeagrassSeagrasses are flowering plants growing in marine or estuarine areas, and Australia is home to over half the world’s known seagrass species. Although there are few accurate data, experts estimate that some 50% of our seagrass beds have been lost since 1788, though patterns vary around the country. In New South Wales an estimated 50% of seagrass beds have been lost in recent decades;1 and at Cockburn Sound in Western Australia, 97% of seagrass beds have been lost.13 Turbidity, from soil erosion, is believed to be one factor behind the decline (the soil prevents sunlight from reaching the sea bed).

Seagrasses provide food for many marine organisms including green turtles and swans, as well as habitats and nursery areas for many fish. Large scale destruction of seagrass areas could have impacts on the commercial viability of the surrounding fisheries. Dugongs are particularly at risk from the loss of seagrasses, which are the sole source of food for this large marine mammal. The loss of seagrasses, as well as accidental capture in mesh nets, has led to the dramatic decline of some populations of dugongs since 1800.11

Coral reefsAustralia has two major coral reefs: the Great Barrier Reef, which at 2,500 km long is the largest coral reef system in the world, and Ningaloo Reef in Western Australia which stretches for 230 km. Both are diverse marine systems that are home to many organisms, and provide commercial benefits to Australia, mainly through tourism and fishing.

As with many marine systems and species, coral reefs are potentially at risk from international as well as domestic influences. Rising sea temperatures (linked in part by some scientists to greenhouse gases) could place reefs at risk from coral bleaching, which occurs when water temperatures exceed long term averages by 1.5 șC-2 șC. Once this temperature threshold is exceeded, algae in the coral tissues are expelled, allowing the white skeleton to show through the clear tissue cover. If temperatures remain above normal levels for more than a few weeks the coral can die. On reefs where the majority of corals die, the plants and animals that depend on a healthy reef lose their habitat and a wide variety of biodiversity is lost. Widespread bleaching events occurred in Australia in 1998 and 2002, causing extensive stress throughout the entire reef ecosystems. Although Australia was not affected as badly as other regions, a small proportion of reefs was severely damaged in each bleaching event. For example, 70%-90% of corals were killed by bleaching on reefs around Bowen in 2002, and similar coral mortality was reported from reefs in the Coral Sea in 2002 and at Scott Reef off northern Western Australia in 1998.14

Domestic sources placing the Great Barrier Reef at risk are sediment and nutrient runoff (often from land use practices far inland), commercial and recreational overfishing, and the coral-eating Crown-of-Thorns Starfish, which periodically explodes in numbers. Scientists are still unsure what triggers the starfish outbreaks, although some theorise that overfishing of the starfish's natural predators or increased nutrient levels in the water from pollution are to blame.15

Sources of reported oil spills, 2002-2003

The environmental impact of oil spills depends largely on the size of the spill, the location of the accident and the prevailing weather conditions at the time: oil spills close to the coast or near areas of high conservation value are likely to cause the greatest damage. Between 1994-95 and 2002-03 there were over 2,800 oil spill sightings in Australian waters. In 2002-03, 300 oil discharge sightings and oil spills were reported (graph above) where 77 of these incidents required a response action under the National Plan arrangement.16

Although many invasive species are difficult to eradicate, the removal of Black Striped Mussels from Darwin Harbour in 1999 was effective, albeit costly. These mussels grow in dense mats and an individual can produce 50,000 offspring in a month. They were probably transported to Darwin on the hull of a yacht. If established, they could have threatened the biodiversity of surrounding waters, had a major impact on aquaculture, commercial and recreational fishing and could potentially have affected the local port and shipping industries, through the fouling of wharves, marinas and vessels. The mussels' freshwater cousin which behaves similarly, the Zebra Mussel, caused very significant economic and ecological damage to the North American Great Lakes. The removal operation involved treating three infected marinas and numerous vessels that were thought possibly to be infected.17

Water quality

In 2001, experts on the State of the Environment Committee indicated that the maintenance or restoration of water quality, particularly in coastal waters, is a critical marine environmental issue in Australia. Although they assessed that many coastal areas have excellent water quality, they also assessed that many areas do not.11

Poor water quality can be attributed to many sources, sometimes land use practices far inland that add nutrients to inland waters (such as land clearance or overgrazing which can enhance erosion or the use of agricultural chemicals).

Protecting our oceansA number of initiatives are underway to give greater protection to Australian oceans.

The National Representative System of Marine Protected Areas (NRSMPA) is setting up a system of marine protected areas that are established under law to protect biodiversity and natural and cultural resources.Developed cooperatively by the Commonwealth, the states and the Northern Territory, the NRSMPA aims to build a system of marine protected areas that is

Comprehensive: sampling the full range of Australia's ecosystems.

Adequate: to ensure the conservation of marine biodiversity and integrity of ecological processes.

Representative: including marine protected areas that reflect the marine life and habitats of the area they are chosen to represent.

Meanwhile, a series of regional marine plans are being prepared to identify priorities and short-list areas that should be assessed for declaration as a marine protected area.

Scientists are working to gather better information about the condition of existing protected areas.In 2003-03, for instance, the Commonwealth trialled a new approach of monitoring its marine protected areas, by developing key indicators of ecosystem health in six coral reef reserves.

Nitrogen and phosphorus are found naturally in inland and coastal waters, but in large quantities they contribute to the increase in estuarine algal blooms. Toxic algal blooms kill fish, and plants can die because of decreased sunlight. They also affect human health by making seafood unsafe to eat and water unfit for recreational purposes.

Sewage discharged into seas releases nutrients and, sometimes, disease-causing micro-organisms, which can make water dangerous to swim in or seafood dangerous to eat. High levels of disease- causing bacteria and viruses can cause problems such as gastroenteritis, respiratory infections and hepatitis.

The improvements in the disposal and treatment of sewage at Sydney's sewage outfalls saw a reduction in levels of certain bacteria (bacteria called coliforms) between 1989-90 and 1999-2000. None of the 23 beaches tested had a coliform density above health guidelines in the summer of 1999-2000. In 1989-90, 11 had exceeded the limit.18

Endnotes

1. Zann, L. 1995, Our Sea, Our Future: Major Findings of the State of the Marine Environment Report for Australia, Great Barrier Reef Marine Park Authority for the Department of the Environment, Sport and Territories, Ocean Rescue Program 2000, Townsville.